TOPIC: CUT
Something to try when you get a message like this caused by a filename with a leading hyphen: "mv: illegal option -- u"
3rd December 2024Recently, I downloaded some WEBP files from Ideogram and attempted to move them to another folder. That is when I got the message that you see in the title of this entry. Because I had not looked at the filenames, I baffled when I got this from a simple command that I had been using with some success until then. Because I was using an iMac, I tried the suggestion of installing coreutils to get GNU mv and cp to see if that would help:
brew install coreutils
The above command gave me gmv and gcp for the GNU versions of mv and cp that comes with macOS. Trying gmv only got me the following message:
gmv: cannot combine --backup with --exchange, -n, or --update=none-fail
The ls command could list all files, but not the WEBP ones. Thus, I executed the following to show what I wanted:
ls | grep -i webp
That got around the problem by doing a subset of the directory listing. It was then that I spotted the leading hyphen. To avoid the problem tripping me up again, I renamed the offending file using this command:
mv -- -iunS9U4RFevWpaju6ArIQ.webp iunS9U4RFevWpaju6ArIQ.webp
Here, the -- switch tells the mv command not to look for any more options and only to expect filenames. When I tried enclosing the filename in quotes, I still got problems, even that might have because I was using double quotes instead of single quotes. Another option is to escape the leading hyphen like this:
mv ./-iunS9U4RFevWpaju6ArIQ.webp iunS9U4RFevWpaju6ArIQ.webp
Once the offending file was renamed, I could move the files to their final location. That could have used the -- option too, saving me an extra command, only for my wanting this not to trip me up again. Naturally, working in Finder might have avoided all this as much as not having a file with a leading hyphen in its name, but there would have been nothing to learn then.
Removing duplicate characters from strings using BASH scripting
30th March 2023Recently, I wanted to extract some text from the Linux command by word number only for multiple spaces to make things less predictable. The solution was to remove the duplicate spaces. This can be done using sed, but you add the complexity of regular expressions if you opt for that solution. Instead, the tr command offers a neater approach. For removing duplicate spaces, the command takes the following form:
echo "test test" | tr -s " "
Since I was piping some text to the command, that is what I have above. The tr command is intended to replace or delete characters, and the -s switch is a shorthand for --squeeze-repeats. The actual character to be deduplicated is passed in quotes at the end; here, it is a space, but it could be anything that is duplicated. The resulting text in this example becomes:
test test
After the processing, there is now only one space separating the two words, which is the solution that I sought. It certainly cut out any variability that I was encountering in my usage.
Picking out a word from a string by its position using BASH scripting
28th March 2023My wanting to execute one command using the text output of another recently got me wondering about picking out a block of characters using its position in a space-delimited list. All this needed to be done from the Linux command line or in a shell script. The output text took a form like the following:
text1 text2 text3 text4
What I wanted in my case was something like the third word above. The solution was to use the cut command with the -d (for delimiter) and -f (for field number) switches. The following yields text3 as the output:
echo "text1 text2 text3 text4" | cut -d " " -f 3
Here, the delimiter is the space character, but it can be anything that is relevant for the string in question. Then, the "3" picks out the required block of text. For this to work, the text needs to be organised consistently and for the delimiters never to be duplicated, though there is a way of dealing with the latter as well.